Pressure indicating method and apparatus



July 27, 1943 H. o. ELFTMAN PRESSURE INDICATING METHOD AND APPARATUS Filed Jan. 9, 1942 2 Sheets-Sheet 1 l t gg l Illlmmnmmnlmlmmmmlmmlllmlmmmlr July 27, 1943. H. Ov. ELFTMAN 2,325,490

PRESSURE INDICATING METHOD AND APPARATUS Filed Jan. 9. 1942 2 sheets-sheet 2 painted reflective surface thereon a not in contact with the face II of the plate. Y The Pliolm being thus directly against the plate and not the painted vor 'reflective surface, the paint is not in dangerV of -sticking vtothe plate, 4'thus allowing of time. 1

Additionally, this reflecting "surraeelniust be face mayY befformedv fromfpar-ticles of reflective through the vertical edges I'I of that plate. One satisfactory manner of achieving this arrangement is to mount lamp supporting brackets 23 onthe inside of casingfv I2d"- adjacent the side edges Ilof the plate I5, these `brackets, in turn non-pressure positions to be restored when the Y pressure is removed. Over this layer of Plioillm,`

holding lamp velements 24 which are connected to a source of electrical supply by conductors 25.

` Va further layer of Pliofllm 2 Ilb"isiplaced*which` layer serves to protect the painted reflectivesurf face and thus enables good reflective qualitiesv of the material to be retained for long periods 'Y of -the four sides of the plate.

materials errlbedded;I in plastics' or ,other substances, whereby a greater diffusionof, light may `inasmuchfas ,the impertent object is; tearing the reflective material into intimate, ContactY with the Yplate at thegpoints of appliedV pressure, the

object whose :pressure is sought mayA be placed vdirectly Von this-materiale; Qn the other hand,

if desired, there;-may be interposedbetween thisv reflective material and the lobject whose pressure points are ,sought,an intermediate pressure receiving mat., It is tobe remembered, however, that the interpositioning *ofl this matmay *not be essential and may or may. not be usedvas desired.

material capable of being deformed and `then returning toits original shape lThe irregular con- `tours of .the `mat2I rest upon thereflective marenal, while the. eppesltelyeispesed face .ef this mat is thesurface upon which' the object Whose' pressures are to be .noted is placed. TheY form of thermal-,illustrated in theFgs, .2,A 3,* 4 andi/5 As showmf-Ithe'refis'interposed 4a. mat ZIrnader l of a flexible materialrsuch asrubber, felt or other 35V consists of ,a 'rubber matwithcthe lower surface comprising aik groupmoff, pyramid shaped projec,

tions 27 Ia with their apexesslightly flattened; It

is, ofcourse, apparent that pressurepn the upper or -ilatsurface vof thatvmat. will cause the apexesof Vthepyramids lto begpushed towards the plate I5, v-tllus causing the intermediary renee.

' tive surface 2 3 .,-tofbe broughtinto more intimate ,contactY with the ,,upper {surface I.'I Vof the plate I5 'and eliminating atthat point `the vnormal air dividing; space, Due to the knatural flexibility of thepressuregrnatzl, it isfapparent that. the,- greater `the pressure, the more will the' vapex of l,the pyramids ,bei compressed, e and lconsequently the broader area of contact which they will cause Vthe reflective surface 20 to make with theplate I5. Fig. 5illustratesethe l.varying Vs ize'images22.

. which the. pressure', -areasof the. pyramids create f and the mannereinwhiehfthe pressure areas. and

degree ,may 'beviewedb'y-an observer. hesmaller areas 22gindicate less appliedpressure on Ythe pressure matfatthos-epoints than V at the pQin'tsL` of larger,areas.-

' ,It is off course, clear- L ,'rnain' purpose ,ofthev present f invention is t0 provide Va ,means rand method ot-seeing the pointslofcontactrZZ whichfare cre'a,ted. v :Accordinglmgsthe vprovisiony ofV light sourceswhereby fthe points 22ywill, be readily visible is-v one .Lof .the major: objects `of Refleotorsl mounted on casing l2a by means i of brackets 21 serve to reflect the light from the lamps 2t through the vertical edges of the plate I5. `If desired, a single light source might be s utilize d, or,light sources might be placed on each tion'intopractice. Whilel believe that this Specification and, above ,des'cription will Venable those skilled inthe art Ytov readily follow my invention, Irnevertheless` desire to explain the reasonV for the lighted areas, a'sunderstancl it.

VItis believedjthat the critical angle, for the 'total reliection oflight in either glass or Lucite, lboth of which substances arehighly adaptable to form the transparent plate I5, is less than 45 degrees. In view of, this, light which enters the plate I5 through the vertical side edges'I'I, will .upon 'reaching thehpper horizontal plate-air boundary 'surface'and `before a'reilectiye surface is pressed yagainstjitybevtotally reflected therefrom, and as ,this light'travels inside ofthe plate I I to thev lower horizontal plate-'air'jboundary I8, it will' again beltotally reflected'from' YVthis lower horizontal' face'g'of the plate,`jand consequently'this light willno'temerge from'y the lower Vsurface'of the plate.' `QI-Iowever,A (referring now ,to the case where thepa'inted surface of the Yrelective material 4is` notin Contact with the transparent plate),when Athe reilective surfacell is `pressed into contact with` the vrtransparent plate I5 by means lof pressure being applied divrectlyto itasinthe case where'theobjectrests directly'onv the reiiective surface orby means of the vinterposed pressurelmat, if one is used, .the index `of 'refraction ofthe y`material whichis pressed into contactwith the' transparent plate,

Yas well as theindex of refraction of the `transparent plate, must be considered together and the critical angleffor total reection is increased.

VUnder these conditions, some of vthe' light which reachesfthe upper surfacehof the Atransparent l plate is "refracted' into" the superimposed ,sub-

stance and is then reflected by either the superimposed substance itself, or` Yby the reflecting surface 20a, whichi's on the vuper surface ofthe superimposed substanceV 2l). `If thisjadditional reiiecting .surface vwas perfectlyV parallel 'to the uppersurface ofthe plate, very little would be gained, sincelthelight reected from it would .pursue a course parallel k.tothatoffthe reected rays, if there had been Ano superimposedlsubstance, and accordingly, would again notleave the lower surface* oftheplate. How'evei, since Y the reflecting surface of the materials mentioned,

` 2,325,490 of the transparent plate. It is these diffused rays which come from the areas of contact 22,

which cause the areas of contact to appear light K against a dark background.

While the above explanation discussed a situ ation in which the painted area was spaced from the transparent plate, the same situation and explanation applies to the case where the painted or reflective surface is directly adjacent to the plate with the exception that the light rays then do not pass through a superimposed subtance before reflection.

It is to be borne in mind that since the lighted areas are due to reflected light, a shaping or bevelling of the vertical surfaces through which the light enters, in a degree dependent upon the index of refraction of thev transparent plate, might be utilized to cause the light rays to reect with greater intensity and changes of this nature which are known to those skilled in the art, are broadly within the teachings of my invention.

In one form of my invention, the points of pressure contact 22 may be made to appear as darkened against a lighter background, rather than light as has previously been described. In this form, the only difference is that the light source is not passed through the vertical side edges of the glass or Lucite plate, but through the lower horizontal surface. These darkened points of pressure contact may have their contrast with' the light reflective material increased i if the raised portions of the mat which is pressing against the reflecting sheet contrast in color with the reflective sheet and provided of course, that the reflecting sheet allows part of the light to penetrate through it. The primary eifect, however, of the darkened areas is not due to this color contrast, but merely to the scattering of the light entering from below the 'bottom horizontal plane surface and reflected from the contact area.

Where a pressure mat is used, its form may be varied so long as the essentials of the raised, flexible areas is present. In Fig. 7 there is illustrated a desirable form of rubber mat 28 comprising raised round projections 23a. The shape and area of the raised portions as well as their flexibility may be varied according to the pressures to be applied.

In'order to provide means of viewing the pressure areas without having to look upward on the underside of the transparent plate, I have provided the apparatus with a mirror 29 which is hinged in the frame IU by means of pin 38 and adapted for swinging adjustable movement so as to rest against stop 3l which may be constructed for placement in varying positions. By this means the image is projected forward to an observer or where desired, a camera 32 may be mounted in front of the apparatus for the photographic recording of the pressure areas.

'I'he mode of operation of the method and apparatus is obvious from the above, and accordingly, is not separately described. Having now set forth my invention, I Wish it understood that I do not limit myself to the specific embodiments herein described, except as may be required by the appended claims.

I claim:

1. An apparatus for creating visual areas corresponding to areas of applied pressure, comprising a transparent plate, a solid-resilient light reective material overlying and normally partially spaced from said plate, a light source directed through said plate, and to said reflective surface, whereby when areas of pressure press said reflective material into contact with said plate, said pressed'areas appear in visual contrast to unpressed areas.

2. An apparatus for creating visual areas corresponding to areas of applied pressure, comprising a transparent plate having side edges and substantially horizontal upper and lower faces, a solid resilient light reflective sheet material overlying and normally partially spaced from said upper face, a light source directed through a side edge of said plate, whereby when areas of pressure compress said reective material into contact with said plate, light rays from saidlight source which had previously not reflected from said upper plate surfaces to and through said lower plate surface, now reflect from said upper surface or said light reflective material and pass through the lower surface of said plate.

3. A device for changing physical pressures to Ylighted areas comprising a transparent plate having side Vedges andsubstantially horizontal and spaced top and bottom faces, a light source directing light into said plate, a translucent solid resilient reflective material lying on said upper horizontally disposed face and in normal unpressed engagement therewith, whereby when areas of pressure press said translucent reflective material into contact with said plate, said points of contact create reflective areas characterized by their capability of reiiecting light to pass through the lower horizontal face of said plate, which light had previously been unable to pass through said face.

4. AnV apparatus for creating visual areas corresponding to points of applied pressure comprising a transparent plate, means for illuminating said plate, solid resilient reflective means superimposed on said plate, a pressure mat superimposed on said reflective means, and raised areas carried by said mat and in contact with said refiective means and adapted to press said reflective means into contact with said transparent plate.

5. An apparatus for creating visual Yareas corresponding to points of applied pressure comprising a transparent plate, means for illuminating said plate, resilient reflective means, a pressure mat superimposed on said reflective means, raised areas carried by said mat and in contact with said reflective means and adapted to press said reflective means into contact with said transparent plate, and a mirror angularly disposed with reference to said transparent plate and adapted to receive and reflect images appearing on said plate.

6. An apparatus for creating visual areas corresponding to areas of applied pressure comprising a transparent plate provided with parallel horizontal surfaces and edge surfaces, a solid light reflective, resilient material loosely overlying said plate, a flexible mat having one surface adaptedV to permit an object to be placed thereon and having the other surface comprising a series of raised exible areas in Contact with said light reflective material, a light source directed through the edges of said transparent plate whereby areas of pressure from an object placed on said mat press said reflective material into contact with said plate, said pressed areas thereby reecting said light at angles permitting said 

